1. Field of the Invention
This invention relates to a photosensitive element used for a silver salt diffusion transfer process and capable of providing an image of good quality.
2. Prior Art of the Invention
Processes for forming an image by silver salt diffusion transfer are well-known. A general example of the procedure of the process is as follows. An exposed photosensitive silver halide emulsion layer is first processed with an aqueous alkaline solution containing a developing agent and a silver halide solvent. The exposed silver halide grains are reduced to silver by the developing agent, while the unexposed silver halide grains are converted to a transferable silver complex salt by the silver halide solvent. This silver complex salt is diffused and transferred by inhibition to a layer containing silver-precipitating nuclei (an image-receiving layer) laid over the emulsion layer, where the silver complex salt is reduced by the developing agent with the aid of the silver-precipitating nuclei, to provide a silver image.
In practicing this process, there is usually used a film unit which comprises a combination of (i) a photosensitive element containing a layer of photosensitive silver halide emulsion on a support, (ii) an image-receiving element which includes an image-receiving layer containing silver-precipitating nuclei on a support, and (iii) a processing element which consists of a breakable container which holds a viscous aqueous alkaline solution containing a developing agent, a silver halide solvent, and a thickener. The emulsion layer of the photosensitive element (i) is first exposed, then the photosensitive element is placed over the image-receiving element in such a way that the emulsion layer is against the image-receiving layer of the image-receiving element (ii), and these layers are passed between a pair of rollers so that the processing elment (iii) is broken and the viscous aqueous alkaline solution it contains can spread, and are then allowed to stand for a predetermined time. The image-receiving element (ii) is then peeled off the photosensitive element (i) to provide a print comprising the image-receiving layer in which the desired image has been formed.
As for the image-receiving element used for the silver salt diffusion transfer process, Japanese Patent Publication No. 32754/1969 discloses an image-receiving element prepared as follows. A silver-precipitating agent is added to an alkali non-permeability polymer by vacuum metallizing and thereafter, such a polymer is dissolved in the solvent in order to be applied to a support. After drying, a chemical treatment such as hydrolysis is applied to the surface layer of such a polymer so that the surface layer has an alkali permeability, whereby an image-receiving element is prepared. Japanese Patent Publication No. 49411/1976 also discloses a method in which during or after oxidazation of a cellulose ester layer, a silver-precipitating agent is embedded in such an ester layer. U.S. Pat. No. 3,671,241 discloses another method in which an image-receiving layer is prepared by saponificating a cellulose ester layer containing a silver-precipitating agent.
On the other hand, for the purpose of obtaining a high quality image by making the grains of the formed image fine, it is well known to use silver halide grains of fine grain size. In particular, for making an ordinary black and white negative photosensitive material, silver halide grains of large grain size and small grain size are used and the emulsion layer containing the silver halide grains of large grain size is provided toward the exposure side from the emulsion layer containing the silver halide grains of small grain size. Although the above-mentioned method has been applied for preparing photosensitive materials for image formation by the silver salt diffusion transfer process, it is not capable of providing a high-sensitivity photosensitive element. Accordingly, an image having fine graininess could not be obtained.